Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Conventional imagers run continuously in order to be available to acquire an image at all times. This requires the panel to consume relative high amount of power. A wireless detector of an imager that operates in a full-power charge integration mode poses a severe constraint on battery life. If a wired panel of the imager is run in an idle mode, it can generally be armed to acquire an image in conjunction with arming the X-ray generator. On the other hand, a wireless panel is not typically in direct communication with the X-Ray generator. Therefore, an idle imager typically has no direct way of knowing when the X-rays may arrive to turn on the panel to acquire an image.
One prior art method of auto-sensing involves acquiring images under the command of a PC host and downstream software used to sort out which images contain actual X-ray image information. Signals developed on the panel itself are used as a means to trigger image acquisition. One prior art approach is to maintain the thin film transistor (TFT) switches in the pixel array at a turned-off condition and sense the bias current when the X-rays turn on. This has at least the following problems: the bias current is only a small fraction of the total photocurrent (<1%) when the TFT switches are shut off, this being the current which charges the parasitic capacitances of the photodiodes to the gate lines and the data lines. This is typically less than 1% of the photocurrent which charges the pixel floating nodes themselves. It is simulated that the bias current flowing during X-ray exposure when the TFT switches are turned off is about 10-1000 nA under typical X-ray conditions, which will be rather difficult to detect above the dark-current background and panel noise. A second issue is that if the TFT switches are held off for long periods of time in the absence of X-rays, the pixels will integrate sensor dark currents and eventually saturate the array in a few minutes. This means that the pixels need to be continuously refreshed every few seconds, and this refresh action could potentially interfere with the unknown arrival of an X-ray pulse.